Variable inductance device



Jan. 17, 1939. A. WEIS VARIABLE INDUCTANCE DEVICE Filed Jan. 6, 1936 INVENTOR ADOLF ATTORNEY Patented Jan. 1 7, 1939 UNITED STATES PATENT OFFICE 2,144.35: VARIABLE INDUCTANCE nsvrcs of Germany Application January 6, 1936, Serial No. 57,689 In Germany January 8, 1935 1 Claim.

Regulable or adjustable inductance coils comprising the use of ferro-magnetic materials have in the prior art been made in this manner that a core consisting of finely-divided magnetic sub- 5 stance made in the same way as the so-called compressed dust-cores, is shifted upon the coil.

Arrangements of this kind involve the drawback that, as a result of appreciable stray or leakage,

the provision of a shielding case or can is imperative.

ciably increased. Another disadvantage is that with coil schemes of the said sort only small inductance changes are feasible.

A far more advantageous solution of the problem is disclosed in the present invention which consists in that RF coils of variable inductance comprising the use of ferro-magnetic materials of the kind used in molded or compressed dustcores is furnished with a single-layer coil winding which is 'firmly arranged .inside a shell of magnetic material and which comprises a body of like material which is capable of being shifted in relation to the shell. The body designed to bring about a change in; the inductance may be 26 rod or pin shaped, and may be introducible into the interior of the coil. For manufacturing reasons, it has proved advantageous to make the said In such case it will be found rodlet of square for. convenient either to wrap the coil also upon a 30 quadrangular coil form or supporting or else to use a circular one in which may be introduced the square rodlet pasted or cemented fast inside a cylinder of insulation material.

Owing to the fact that the coil winding is entirely enveloped on the outside with an envelope consisting of magnetic material, there is not only insured a very efiicient shielding, but at the same time the stray of the coil is appreciably diminished so that distinct shielding means may be dispensed with. As a result the novel arrangement here disclosed distinguishes itself by particularly high freedom from losses. In the'case of great changes of inductance it has turned out to be of advantage to make the coil winding of rather great length compared with its diameter so that transverse-field losses are considerably diminished, and that only the question of minimization of the D. C. resistance and eddy-current losses need to be given any special attention in manufacture. A preferable ratio between coil diameter and length is 1:7. In this manner, the changes of inductance between the starting or initial position of the introducible core, 1. e., outside the coil, and the final position, i. e., when 56 completely introduced in the coil. are at the ratio And this means that the losses are appre- 'eifected most simply by that the coil is sprayed,

all around with the insulation material. what could be used for this purpose to great advantage is a magnetic material manufactured with 15 Troiitul (or a Trolitul matrix or base). From the same material, also by molding or by spraying, the core could be fashioned. Ii.- desired, the

' material used for the core could contain a. larger percentage of iron in order to insure a higher 20 permeability.

The construction of a coil arrangement as here disclosed shall be explained in more detail in what follows by reference to the exemplified embodiment shown in the annexed drawing. 2s

1 denotes the coil winding which is preferably single-layered, and which most conveniently has a length seven times its diameter. The winding is wrapped most conveniently upon a coil form 2 made from insulation material of the low-loss type. say. Trolitul, and the same. is then surrounded with an envelope I consisting of ferromagnetic material as shown in the drawing. As already pointed out above, the said envelope, on the one hand, acts as a shield, while, on the 35 other hand, it diminishes the stray field of the coil so that, whenever necessary, the provision of distinct shielding cases or cans could be dispensed with. By the aid of the saidenvelope, the field of the coil is closed snugly around the coil 40 itself, contradistinct from what is usually true of normal coils wherein the field spreads over a larger region.

4 designates the body designed to be introduced into the coil and made from finely divid- 45 ed magnetic material whose permeability, if necessary, may be higher than that of the envelope. According to the depth of introduction of the rodlet or pin into the interior of the coil, different inductance values will be obtained. In 50 conjunction with a fixed condenser, as will thus be seen, it is possible to form with the novel 0011 an oscillatory circuit which is varied or tuned to different wave-lengths by changing the inductance value of the coil rather than by a varia- K would not do to shift the rodlet at a uniform tion of capacity. Oscillatory circuits 01' this kind may be used in broadcast receiving sets and other high-frequency apparatus.

Inasmuch as it is desirable that the frequency change or an oscillation circuit should be uniform (in accordance with a. straight-line law) in order that, in broadcast receiver sets, uniform division of the dials or scales may be insured, it

rate into the interior of the coil. In fact, for eifecting the shift there is provided a setting mechanism which insures such shift in accordance with a certain law. With this end in view,

for instance, the equalizing or balancing rodlet is coupled with a journaled cam disk 5 which presents a curvature insuring the desired change of the inductance. In the exemplified embodiment here shown, the said disk is otrenifqrm shape known from rotary condenser plates. In order that the core may be kept constantly in connection with the curved cam surface it is advantageous to apply the same firmly against the slope 8 of the cam subject to spring pressure. For this purpose, in the simplest case, there is provided a leaf spring I which engages in a recess of the-balancing or adjusting rodlet or at some projection or lug suitably formed for the purpose on the said rodlet 8. At its opposite end the 'spring (subject to a biasing tension) is secured on some fixed point of supporting 9 which bears the entire coil arrangement.

I .claim:

An inductance device comprising a spindle made of low loss insulation material, an inductance coil wound tightly around the spindle and an envelope tightly surrounding the coil, said i envelope being made of finely divided magnetic material mixed with a binder, a rod constructed of finely divided magnetic material mixed with a binder, said rod being adjustably mounted so that substantially its full length may be inserted within the hollow core of the spindle and removed therefrom, for providing a means for adjusting the inductance value of the coil, said coil having a ratio of its diameter to its length of the order of one to seven whereby the inductance device has very low transverse-field losses and a high ratio of change of inductance.

ADOLF WEIS. 

